The term intaglio comes from the Italian word intagliare, meaning "to incise". In this technique, acid or a pointed tool is used to incise the composition into a metal plate, usually made of copper, but sometimes of steel, iron or zinc. After the image has been drawn, the plate is covered with ink, and then wiped so that only the incised areas contain ink. The pressure of the press forces the paper into the incisions where they pick up the ink, resulting in the raised character of the lines on the impression. Because often the sheet of paper is larger than the plate, an indentation of the plate edges, or platemark, appears around the edges of the image area. Before it became common practice to coat plates with steel for reinforcement, a plate, especially one containing drypoint lines, would degrade over time as the pressure of the press would dull the burr. As a result, the first impression was often crisper than the last and in turn, the edition was numbered in order. The different types of intaglio prints are distinguished by the technique used: etching, aquatint, and photogravure are made using acid to corrode the metal plate, while engraving, drypoint, and mezzotint are made using a sharp tool to incise, or scratch, the surface of the plate. Often several different intaglio techniques are used in the same print to achieve variations in contrast and tone.